1. Field of the Invention
The present invention relates to a semiconductor device and a method of production of the same, more particularly relates to a semiconductor device produced by forming external connection terminals on an electrode formation surface of a semiconductor wafer and a method of production of the same.
2. Description of the Related Art
FIGS. 12A to 12I show a method of production of a semiconductor device formed with metal posts as external connection terminals on an electrode formation surface of a semiconductor wafer. In this method of production, first, an electrode formation surface of a semiconductor wafer 10 from which electrodes 12 are exposed and which is covered by a passivation film 14 (FIG. 12A) is covered with a conductive layer 16 by sputtering (FIG. 12B). Next, the surface of the conductive layer 16 is covered by a photosensitive resist 18 (FIG. 12C), then the photosensitive resist 18 is exposed and developed to expose portions for forming interconnection patterns at the surface of the conductive layer 16 (FIG. 12D).
The electrodes 12 are arranged at an extremely high density at for example the periphery of the electrode formation surface of the semiconductor wafer 10. As shown in FIG. 12E, the interconnection patterns 20 are formed by electroplating the exposed surfaces of the conductive layer 16 by copper. The interconnection patterns 20 are formed led out from the electrodes 12 so as to secure spaces for arrangement of the external connection terminals.
Next, the photosensitive resist 18 is removed and the surfaces of the interconnection patterns 20 and conductive layer 16 are covered by a dry film 22 (FIG. 12F), This dry film 22 is for forming the copper posts 24 forming the external connection terminals (FIG. 12G). The dry film 22 is exposed and developed to form holes for plating at portions for forming the copper posts 24 on the interconnection patterns 20. By electroplating these portions by copper, copper is built up in the plating holes and metal posts 24 of heights of about 100 xcexcm are formed. Next, the surfaces of the copper posts 24 are successively plated by nickel, palladium, etc. to form the barrier layers 26.
The dry film 22 is removed, then the portions of the conductive layer 16 exposed at the electrode formation surface are removed by etching (FIG. 12H). In this way, the electrode formation surface of the semiconductor wafer 10 is formed with copper posts 24 electrically connected with the electrodes 12 through the interconnection patterns 20.
Next, as shown in FIG. 12I, the electrode formation surface of the semiconductor wafer 10 is covered with a resin 28 for sealing. The resin 28 is formed to substantially the same thickness as the copper posts 24. The end faces of the copper posts 24 are exposed at the surface of the resin 28. After the resin sealing, solder balls are placed on the surfaces of the barrier layers 26 and the solder made to reflow to form solder bumps (not shown). Finally, the semiconductor wafer 10 can be diced along with the resin 28 to obtain chip-sized semiconductor devices.
FIGS. 13A to 13I show another method for producing a chip-sized semiconductor device. The semiconductor device obtained by this method of production has gold wires bent in L-shapes for use as external connection terminals. The steps shown in FIGS. 13A to 13E are basically no different from the steps shown in the above FIGS. 12A to 12E. In this method, however, the interconnection patterns 20 are not sealed by resin. The interconnection patterns 20 are formed by gold plating so as to enable them to be left as they are exposed at the outside surface of the semiconductor device.
As shown in FIG. 13F, the photosensitive resist 18 (FIG. 13E) is removed. Next, as shown in FIG. 13G, the electrode formation surface is covered by a resist, then holes 30a are formed in the interconnection patterns 20 at portions for later bonding of the gold wires. The electrode formation surface is covered by the resist 30 so as to cover only the outer surfaces of the gold wires with reinforcement plating after bonding the gold wires. As shown in FIG. 13H, the gold wires are bonded to the interconnection patterns 20 in register with the openings 30a (FIG. 13G). Next, the gold wires are bent into L-shapes and the ends thereof are cut off to form the external connection terminals 32. The outer surfaces of the gold wires are plated to reinforce the wires (the plating material is not shown in the drawing), then the resist 30 is removed and, as shown in FIG. 13I, the exposed portions of the conductive layer 16 are removed by etching.
In this way, the electrode formation surface of the semiconductor wafer 10 is formed with external connection terminals 32 electrically connected with the electrodes 12 through the interconnection patterns 20. Finally, the semiconductor wafer 10 is diced to obtain semiconductor devices provided with external connection terminals 32 comprised of wires bent into L-shapes.
In the examples shown in the above FIGS. 12A to 12I and FIGS. 13A to 13I, the conductive layer 16 was formed on the passivation film 14, but it is also possible to cover the passivation film 14 by a polyimide film and form the conductive layer 16 on the surface of the polyimide film.
Steps for producing a semiconductor device using the above copper posts as external connection terminals and steps for producing a semiconductor device using gold wires bent into L-shapes as external connection terminals are shown in FIGS. 14 and 15. The steps produce chip-sized semiconductor devices by processing the semiconductor wafer to form external connection terminals electrically connected to the electrode terminals formed on it, then dicing the semiconductor wafer. In this way, the methods of the prior art utilize complicated steps, so there are the problems that the production efficiency is reduced and the manufacturing costs increased.
Further, there have been the following problems when mounting a semiconductor device produced by a method of production of the prior art to a board: When mounting a semiconductor device using copper posts as external connection terminals by solder, the solder does not form meniscuses and the external connection terminals are not reliably bonded with the board. When mounting a semiconductor device provided with external connection terminals formed by bending gold wires in L-shapes, due in part to the fact that the heights of the external connection terminals are about 700 to 800 xcexcm, the semiconductor device and the board are bonded spaced away from each other.
The present invention was made to solve the problems in the methods of production of the prior art for producing semiconductor devices by processing a semiconductor wafer. An object of the present invention is to provide a highly reliable semiconductor device able to be produced by a simpler method and thereby able to improve the production efficiency and able to arrange external connection terminals at a higher density and thereby able to handle a greater number of pins and a method of production of the same.
To attain the above object, according to a first aspect of the present invention, there is provided a semiconductor device provided with semiconductor elements, such as transistors, formed on a semiconductor substrate, external connection terminals connecting these elements to an external circuit, and interconnection patterns connecting electrodes of the semiconductor elements to the external connection terminals, wherein the external connection terminals are formed by wires comprised of a conductive material and the parts of the wires bonded to the interconnection patterns are buried in the metal layer forming the interconnection patterns.
The metal layer forming the interconnection patterns is preferably formed by copper plating, gold plating or the like.
As the wires of the conductive material forming the external connection terminals, it is preferable to use gold wires, copper wires, etc.
More preferably, the metal layer and the wires are fabricated by the same material. Therefore, preferably the metal layer is formed by gold plating and the wires are comprised of gold or the metal layer is formed by copper plating and the wires are comprised of copper.
The external connection terminals can be covered by the material of the metal layer forming the interconnection patterns.
The surface of the semiconductor device where the interconnection patterns are formed can be sealed so as to leave exposed the external connection terminals.
According to a second aspect of the present invention, there is provided a method of production of a semiconductor device provided with semiconductor elements formed on a semiconductor substrate, external connection terminals connecting the elements to an external circuit, and interconnection patterns connecting electrodes of the semiconductor elements to the external connection terminals, comprising the steps of forming a conductive layer on the entire surface of the semiconductor substrate where the electrodes are formed, forming a resist pattern on the surface of the conductive layer exposing the conductive layer at portions where pads to which the external connection terminals are to be connected and the interconnection patterns are to be formed, bonding wires comprised of a conductive material to the conductive layer at portions where the pads are to be formed to form external connection terminals, forming a metal layer at the exposed portions of the conductive layer, removing the resist, and removing the conductive layer exposed by the removal of the resist to form interconnection patterns.
After forming the interconnection patterns, it is possible to seal the surface of the semiconductor device where the interconnection patterns are formed so as to leave exposed the external connection terminals.